The present invention describes a transport and applicator to hold and apply thin film membranes to XRF sample cups.
Spectroscopic analysis (XRF Spectroscopy) utilizes sample cups to contain liquid or powder samples for elemental analysis. Sample cups generally have a thin transparent film bottom and may include a top end formed integral with the cup body known as a single ended design. Alternatively, the sample cup may include a second thin film or be secured at the top end, known as a double open end design. Sample cups are generally delivered to the analyst in parts comprised of a side wall member and complementary secondary member, which members are assembled in combination with a separate thin film component to construct a single sample cup. The sample cup, with its liquid or powder sample contained therein, is then manually transported to an XRF instrument and placed in a holder, thin film bottom down, for analysis.
Prior art thin film has traditionally been available as pre-cut squares or circles sized to cover a sample cup opening or on pre-perforated sheets. This thin film product is generally held on a substrate or interleaf of paper to facilitate handling, static control and application to the sample cup. Such products, however, are not ideal as portions of the thin film remain subject to contamination and static handling issues when attempting to secure the thin film to a sample cup. Furthermore, the thin, non-rigid nature of the product increases the difficulty of handling the product and proper placement on a sample cup without introducing error through placement, wrinkles and creases in the thin film (surface damage), contamination or easy separation of the thin film from the substrate (interleaf) on application.
Another product, as described in U.S. Pat. No. 6,009,766, introduces a carrier frame, consisting of a substrate with a through hole. A thin film is bonded to the substrate. This product is then placed over a sample cup, with the exposed thin film centered over the sample cup. The product requires perforations in the thin film product along the perimeter of the through hole to facilitate separation of the thin film on assembly of the sample cup. While this product introduces a rigid carrier assembly, the mechanism of applying the thin film to the sample cup through the use of perforations and tearing of the thin film on application has serious disadvantages solved by the present invention. The use of perforations affects the structural integrity of the thin film, providing points of stretch and unequal shear forces potentially contributing to inaccurate specimen readings, depending upon the consistency of application. The necessity of perforations to effectuate a separation upon sample cup assembly also introduces complexity in the product design avoided by the present invention. Further, the need to substitute thin films of various properties, or to dimension the frame, through hole and film to accommodate different sample cup designs requires substantial changes in manufacturing the perforated thin film product design. A different thickness film, or film of different mechanical properties will require adaptations in the perforation process or design. Finally, mechanical bonding of the thin film to the carrier frame introduces further complexity into the manufacturing process, serves to disrupt the thin film integrity and offers greater potential to introduce contaminants to the thin film surface during manufacturing or in the application of the product. The present invention avoids these disadvantages, being easily scalable both as to frame and through hole but also in the properties of the thin film.
In view of the prior arts' shortcomings, it is thus desirable to create a thin film transport and applicator which facilitates contaminant-free handling of thin film and contaminant-free application of thin film to the sample cup assembly. It is further desirable that the transport and application system allow transfer of the thin film and its subsequent assembly to occur easily and without any damage to the surface of the thin film to ensure error free XRF analytical testing results of the sample.